According to the Washington Manual of Medical Therapeutics (31st ed.; 2004; Lippincott Williams & Wilkins), liver disorders can be categorized in different groups of diseases, in particular viral diseases, drug- and alcohol-related liver diseases, immune-mediated liver diseases, metabolic liver diseases, miscellaneous diseases such as non-alcoholic fatty liver disease, and complications of hepatic insufficiency (such as fulminant hepatic failure or hepatocellular carcinoma) and of liver transplantation.
In particular, non-alcoholic fatty liver disease (NAFLD) is a common hepatic disorder with histological features of alcohol-induced fatty liver disease in individuals who consume little or no alcohol (Yeh M et al., 2007; Marchesini G et al., 2003). NAFLD is due to the abnormal retention of lipids within cells (commonly defined as steatosis), an event more frequent in liver since this organ is primarily responsible of lipid metabolism. NAFLD has a spectrum of histological forms including hepatic steatosis, and non-alcoholic steatohepatitis (NASH), which is characterized by liver inflammation, steatosis, necrosis and fibrosis due to the disruption of liver cells. Conditions associated with NAFLD are varied, and include type 2 diabetes, obesity, dyslipidemia, metabolic syndrome, treatment with hepatotoxic drugs, toxins, infectious agents, or other exogenous causes.
Although NAFLD typically follows a benign, non-progressive clinical course, NASH is a potentially serious condition; as many as 25% of patients may progress to advanced fibrosis, cirrhosis and experience complications of portal hypertension, liver failure and hepatocellular carcinoma, which makes an early and correct assessment mandatory (Yeh M et al., 2007).
Hepatic imaging systems are useful to evaluate also liver structure and presence of steatosis. However, liver biopsy remains the gold standard for evaluating liver fibrosis, but this method of analysis could not be done for every single study due to its invasiveness. Noninvasive evaluation of liver biochemistry and metabolism is often used to define liver diseases, such as in NAFLD and NASH (Gressner A et al., 2009; Vuppalanchi R and Chalasani N, 2009). By using plasma, high level of enzymes such as Alanine aminotransferase (ALAT), Aspartate aminotransfersase (ASAT), Alkaline Phosphatase (AP), and/or Gamma Glutamyl Transpeptidase (GGT), as well as the presence of other proteins of liver origin (including haptoglobin, total bilirubin, alpha-2-microglobulin, Resistin, cleaved or intact cytokeratin-18) are commonly measured in addition to serum glucose and insulin resistance parameters. Since the level of ALAT activity is frequently increased in NASH patients (Angulo P et al., 2002), this criteria is considered as a surrogate marker for assessing liver injury. In fact, reliable noninvasive methods are not available to correctly diagnose NAFLD or NASH and even the histological features are not always sufficient to distinguish properly NAFLD or NASH from other conditions such as alcoholic liver disease (Yeh M et al., 2007, Vuppalanchi R and Chalasani N, 2009).
Means for an effective treatment for liver fibrotic diseases, and NAFLD and NASH in particular, are still insufficient. No treatment is established for patient with NASH, and several therapeutic options are tested in clinical trial (Vuppalanchi R and Chalasani N, 2009, Dowman J. K et al., 2009). These studies involve the use of many different families of chemical compounds (fibrates, thiazolidinediones, biguanides, statins, cannabinoids) and therapeutic targets (nuclear receptors, angiotensin receptors, cannabinoid receptors, HMG-CoA reductase). Recently, studies involving thiazolidinediones (Rosiglitazone and Pioglitazone) have shown that these drugs may improve liver condition but treatment with these drugs is not without undesired effects such as higher risks of congestive cardiac failure and osteoporosis, as well as weight gain with psychological effects on the patient (Dowman J. K et al., 2009; Shiri-Sverdlov R et al., 2006; Neuschwander-Tetri et al., 2003). Clinical trials involving the administration of cannabinoids have raised the concern of neuropsychiatric disruption (Vuppanchi R and Chalasani N, 2009). Other therapies currently ongoing are seeking to assess in NASH drugs as antioxidants but none of these treatments has yet showed convincing results (Nelson A et al., 2009).
The need for novel therapeutic options for the management of liver disorders, in particular those involving liver fibrosis and/or steatosis, is still clear and urgent.